چکیده انگلیسی

Exception handling in workflow management systems (WFMSs) is a very important problem since it is not possible to specify all possible outcomes and alternatives. Effective reuse of existing exception handlers can greatly help in dealing with workflow exceptions. On the other hand, cooperative support for user-driven computer supported resolution of unexpected exceptions and workflow evolution at run-time is vital for an adaptive WFMS. We have been developing ADOME-WFMS as a comprehensive framework in which the problem of workflow exception handling can be adequately addressed. In this article, we present an adaptive exception manager and its web-based interface for ADOME-WFMS with procedures for supporting the following: reuse of exception handlers, thorough and automated resolution of expected exceptions, effective management of Problem Solving Agents, cooperative exception handling, user-driven computer supported resolution of unexpected exceptions, and workflow evolution.

مقدمه انگلیسی

Workflow management system technology, though recent, has been regarded as one of the main types
of advanced information systems. It is perceived that workflow technology not only requires the support
for complex data model functionality, but also flexibility for dynamically modifying the workflow
specifications, especially in cases of exception handling. Because of unanticipated possibilities, special
cases, and/or changes in requirement and operation environment, exceptions may occur frequently during
the execution of a business process. An exception is an event (i.e., something that happens) that deviates
from normal behavior or may prevent forward progress of a workflow. Upon unexpected exceptions, a
comprehensive WFMS should be able to support the users to reallocate resources (data / object update) or
to amend the workflow, such as adding alternatives (workflow evolution). Further, frequent occurrences
of similar exceptions have to be incorporated into workflow specifications as expected exceptions. Such
workflow evolution can help avoid unnecessary exceptions by eliminating error-prone activities, adding
alternatives, or by enhancing the operation environment. This can lead to a WFMS that supports
workflow adaptation through exceptions.
In contrast with traditional software systems, workflows usually evolve more frequently, making
reuse a vital issue. Reuse of workflow definitions and exception handlers are very important for the
smooth operation of a flexible WFMS. Support for workflow evolution at run-time is vital for an adaptive
WFMS. There have been a few WFMSs designed to address these two problems (viz. reuse issues and
workflow evolution) effectively and adequately. However, none of them is based on a me&modeling
exception-centric approach.
With a meta-modeling approach, we can have a simple but expressive core data dictionary (metaschema).
From this me&level schema, users can define all other classes for the WFMS, including
activity schemas, exceptions and handlers. Further, from these schemas WFMS objects (in particular,
activity instances) can be instantiated. This contributes a substantial improvement to WFMS modeling
based on relational models because the entity modeling and implementation is tied together in a
straightforward manner. Extensive reuse can also be facilitated as discussed in Section 5.
We use an integrated, event-driven approach for execution, coordination, and exception handling in
our WFMS. Events (such as database events I exceptions, or external inputs) trigger the WFMS ExecutionManager to start an activity. The WFMS Execution Manager uses events to trigger execution of tasks,
while finished tasks will inform the Execution Manager with events. A task is executed by a problem
solving agent (PSA) which is a hardware/software system or a human being. Upon an exception,
exception events will trigger the WFMS Exception Manager to take control of resolutions. These
resolutions can trigger a software solution or will involve a human to cooperatively resolve an exception.
An effective user interface is vital to the execution of the above features. We choose to use a webbased
user interface because workflow and agents tends to be widely distributed, even involving other
organizations across the Internet. Mobile clients can be supported (alerted by ICQ or electronic mail) by
the Internet, and they can access the WFMS with a web-browser. Direct message passing between clients
and remote data sharing can be facilitated. On the other hand, web-based tools are a prevailing technology
that has a wide range of utilities and off-the-shelf applications, supporting wide ranges of hardware and
software platforms at a relatively low-cost.
In this regard, we have developed ADOME-WFMS, based-on an Advanced Object Modeling
Environment (ADOME [45]), with a novel exception centric approach. The key features are as follows:
1. Effective coordination of PSAs and an object-oriented capability-based approach to match tasks and
agents;
2. Automatic resolution of expected exceptions and exception driven workflow recovery;
3. Dynamic binding of exception handlers to activities with scoping, and to classes, objects and roles;
4. Addition, deletion and modification of exception handlers at run-time through workflow evolution;
5. Specifying and reusing exception handlers upon unexpected exceptions and system-assisted exception
handling; and
6. Application of workflow evolution and workflow recovery in exception handling.
Thus, adding a web-based user interface allows ADOME-WFMS to effectively support distribution of
PSA and workflow execution even with a centralized control design. In this article, we present a
framework for flexible workflow enactment and online workflow evolution in an advanced object
environment (active OODBMS with role and dynamic schema support), with reference to ADOMEWFMS.
More details regarding classification of exceptions and handlers, and modeling aspects for
ADOME-WFMS are given in [22]. In addition, ADOME-WFMS exception driven workflow recovery
has been presented in [26]. The objectives and contribution of this article include: (i) the mechanism of
ADOME-WFMS and resolution of expected exceptions, (ii) support of reuse for workflow definitions,
constraints, exception types and handlers in ADOME-WFMS, (iii) an augmented solution for exception
handling based on workflow evolution, (iv) management of distributed PSA and allow for distributed
users, (v) user-driven computer supported resolution of unexpected exceptions, and (vi) demonstrating the
use of ADOME-WFMS in supporting exception handling through effective web interface facilities.
The rest of our article is organized as follows. Section 2 presents a me&modeling approach to
activity modeling, which facilitates reuse and workflow evolution. Section 3 presents the architecture of
ADOME-WFMS with web-based PSA coordination and general mechanisms. Section 4 discusses how
ADOME-WFMS resolves for expected exceptions. Section 5 explains how reuse can be facilitated. The
ADOME-WFMS Human Intervention Manager is detailed in Section 6 to illustrate how unexpected
exceptions are handled in ADOME-WFMS, with novel web-based workflow evolution functions.
Section 7 compares related work. Finally, we conclude the article with our plans for further research in
Section 8.

نتیجه گیری انگلیسی

This article has presented adaptive exception handling in ADOME-WFMS, a flexible WFMS based
on an active OODBMS extended with role and rule facilities (viz., ADOME). Compared with other
research on this topic, ADOME provides an advanced object-oriented environment for developing a
WFMS, which can adapt to changing requirements, with extensive support for reuse. In particular, the
resultant system (i.e., ADOME-WFMS) supports a rich taxonomy of exception types and their handling
approaches, and a novel augmented solution for exception handling based on workflow evolution.
Effective reuse of workflow definitions, exceptions, handlers and constraints in ADOME-WFMS are also
possible. This article has also described in detail, how expected exceptions are actually resolved with the
ADOME-WFMS Exception Manager and how unexpected exceptions are handled through its Web
hzterjice. It should be noted that, though exception handling is highly automated in ADOME-WFMS by
scoping, binding and reuse, human intervention management must be provided to support for (totally)
unexpected exceptions and drastic workflow evolutions. Moreover, the Web Interface also demonstrates
effective management of human PSAs, especially during exceptions.
ADOME-WFMS is currently being built on top of the ADOME prototype system, with a web-based
user interface to accommodate the whole range of activities. We are also porting the ADOME-WFMS
Activity Editor to a web-based version to support web-based workflow evolution with full graphics
capability. On the theoretical side, we are looking at reuse models in a more formal way, and the
possibility of applying UML technologies to this aspect. We are also interested in performance
evaluation and optimization of workflow exception handling [39].
Further research issues on interfacing and interoperability are emphasized for extending the
applicability of an advanced WFMS engine, which includes: expanding the possible interfaces and
coordinating different types of agents, graphical workflow evolution tools, and inter-operating with other
WFMS. We are in the process of developing E-ADOME [22], an extension of ADOME-WFMS with
coordination mechanisms for different kinds of agents, in various advanced real-life e-commerce
environments, such as procurement, finance, stock-trading and insurance. We are especially interested in
the RosettaNet Internet business communications standards (a framework using XML to streamline the
computer product and IT supply chain).
Finally, it should be noted that exceptional handling, and especially unexpected exception handling is
a very tough problem which requires an in depth application domain knowledge to build a usable
solution. The solutions elaborated in this paper can be fine-tuned for a specific application domain or area
(as illustrated in [22]) so that such usable and practical systems can be built. In this regard, this paper
describes in detail such a pragmatic solution to the exception-handling problem in workflow management
systems.